Bhagvad Gita is a 701 versed text which is inside Mahabharata. And similarly Durga Saptashati (Sapta =7 and Shat =100) is also 7×100= 700 versed text which is inside Markandeya Purana which is also known as Devi Mahatmya.
One of the most famous and important verse in Bhagvad Gita is Bhagvad Gita Chapter 4 Verse 7, where Lord states to Arjuna as:
यदा यदा हि धर्मस्य ग्लानिर्भवति भारत |
अभ्युत्थानमधर्मस्य तदात्मानं सृजाम्यहम् || 7||
Whenever and wherever there is a decline in righteousness and an increase in unrighteousness, O Arjuna, at that time I manifest myself.
As Devi Mahatmya is also related to destruction of demonic forces by Devi, are there similar statements made by Devi in Durga Saptashati ?